Reflex-reflectorizing composition



United States Patent Office 3,099,637 Patented July 30, 1963 3,099,637 REFLEX-REFLETORHZTNG CQMPQSHTIGN Alfred Nellessen, Rcseville, Minn, assignor to Minnesota Mining and Manufacturing Company, St. Paul,

Minn, a corporation of Delaware No Drawing. Filed Nov. 14, 1958, Ser. No. 773,814 1 Claim. (61. 260-48) This invention relates to a mobile transparent coating composition suitable for use in converting an ordinary reflective surface into a reflex-reflecting one without greatly altering its normal daytime appearance or design.

The composition is adapted to be applied upon a reflective surface by spraying. Immediately upon drying, it provides a coating of a monolayer of tightly compacted transparent micro-spheres in intimate permanently-bonded contact with the underlying surface. The resulting structure serves as a reflex reflector of light, that is, it serves to return light back toward its source in .a brilliant cone with the axis of the cone essentially common with the incident beam of light, even though the incident beam strikes the structure at an angle. Thus, it is apparent that the composition hereof is useful in reflex reflectorizing highway guard rails and posts painted with aluminum or other reflective pigmented paint. Angular or non-normal light on aluminum guard rails and posts is only poorly reflected by such structures; and this invention provides a convenient and economical solution to the problem of brilliantly reflex reflectorizing them quickly in .a practical manner, as by spraying.

A further advantage of this invention is that now, for the first time insofar as we are aware, suitable reflective substrates, even vertical surfaces of in-place structures, may be reflex reflector-ized quickly and economicaly in situ, simply by spraying Without need for special metering devices, or other special conditions designed to assist flow and attachment of glass beads. For example, con crete bridge abutments, embossed metal shapes, corrugated guard rails, cables, and even the underside of overpasses can be easily reflex reflectorized with the product of this invention. Surprisingly, rough irregular surfaces or the forces of gravity do not hinder use of the composition. Other transparent systems are extremely difficult to handle under such circumstances.

Known compositions of transparent glass beads in a transparent varnish vehicle have provided only poor reflex reflection when coated and dried on a reflective base. Beads in such compositions have served largely as centers for providing a lenticular or pebbly surface on drying of the coating. The efiiciency of the beads as retracting and focusing elements per se has been inherently quite limited in the case of such known compositions. Also, beads in such compositions tend to settle on storage of the composition. While the compositions have been satisfactory for use in some screen process techniques of application, where metering of the composition upon a surface is depended upon for pro er orientation of the elements of the composition (andj where spaces between the beads in a monolayer are cu tomary and are inherently formed), they have not been found suitable to form, upon drying after application by spraying, brilliantly reflex-reflecting panels.

In fact, it was believed for some time that it would be impossible to accomplish a monolayer distribution of glass beads in a permanent-bond coating applied by spraying. Ordinarily, spraying is expected to give some irregularity of coating. The attainment of .a monolayer of beads, with such monolayer having a lenticular exposed surface of the proper refractive properties, and with the beads of the monolayer in permanently bonded tangential contact with an underlying reflective surface, is not reasonably What one would expect as an incident to the usual spraying operation.

I have, however, been successful in making a composition which inherently forms, on drying after spray application to a reflective surface, a monolayer of tightly compacted lens elements firmly bonded to the substrate with just the proper relationships for brilliant reflex reflection. My composition, when coated and dried, provides a monolayer of tightly compacted glass microspheres in tangential contact with the underlying surface and with an outer exposed lenticular surface of the proper light refracting characteristics for attainment of brilliant reflex reflection. In addition, I have found a way to formulate my composition so that the glass microspheres remain essentially uniformly distributed throughout the vehicle for usefully long periods in a container, e.g., a year or longer, prior to actual use.

There are several critical relationships between the ele-' ments of my composition. The volume concentration of transparent glass microspheres to transparent varnish nonvolatiles or solids in my composition is especially critical for the attainment of permanent, durable and wearable, brilliantly reflex-reflectorizing coatings. Transparent glass microspheres must account for between and of the total volume of the non-volatile constituents in my composition (i.e., the total volume of varnish non-volatiles or solids and transparent microspheres in my composition). This may be referred to as a required BVC (bead volume concentration) of between 65 and 75%. A BVC higher than 75% results in poor bonding of my reflex reflectorizing layer to a substrate. A BVC lower than 65% seriously hampers brilliancy of reflex reflection, interferes with the required tangential orientation of the microspheres in a monolayer upon a substrate, and essentially converts the function of the transparent microspheres from that of lens elements per se to that of aggregates at which varnish solids concentrate, thus interfering with uniformity of reflex reflection.

An essential feature of my composition is that it becomes mobile upon agitation. It exhibits, upon agitation, a viscosity on the order of rich cream. It is of a thixotropic nature and tends to assume a gel state upon standing, but such condition is easily disrupted by agitation. In the mobile state, ingredients of the composition shift position with relative ease and the composition tends to be flowable, but it does not become soupy or Watery in consistency. The varnish component alone, on agitation, usually has a relatively high viscosity in relation to the content of varnish solids in it; but my work indicates that the relationship of varnish solids to varnish volatiles is not as important as the requirement of mobility of my entire composition upon agitation.

The shelf life of my composition is long; and it may be stored for lengthy periods without adverse results. After lengthy quiescent storage of about one year, I have found that the composition still retains an essentially uniform analysis throughout. The miicrospheres have been found to remain essentially uniformly distributed throughout the composition. Slight increases in the viscosity of the composition (observed immediately after agitation) as a result of storage have not been noticeable or even cause for correction, since the compositions tested have remained of sprayable consistency upon agitation; but where such slight increases might occur, a small amount of volatile solvent for the varnish vehicle may be added to render the composition mobile upon agitation, without upsetting the relationships between the ingredients of my composition as required for sprayability.

Thus, my work indicates that the spraya-bility of my reflect-orizing compositions is much less dependent than what one might expect upon the volatile content of the varnish vehicle and the relationship of varnish solids. to varnish volatiles. While I, in most cases, have found that between about 5 and 30% of the varnish vehicle should be varnish solids for good working and sprayability properties, I have found that varnish solids well outside such a range have given compositions possessing suitable sprayabilit'y and other performance characteristics as described herein. Mobility of the composition during application is an essential requirement, Whether the composition be applied by spraying, brushing, screen processing, dip coating, etc.

For maximum brilliance of reflex reflection under standard or the usual atmospheric conditions, the microspheres in my composition must have a refractive index of about 1.9, and an average diameter of between about 15 and 75 microns, preferably between about 15 and 60 microns. Such micro-spheres contribute to the stability of our composition on storage as well as its sprayability characteristics during use.

The composition may be applied upon a variety of reflective surfaces, e.g., specular metal surfaces, semispecular metal painted surfaces, bright pigmented (e.g., white, yellow, red, etc.) diffuse reflecting surfaces, etc. Maximum reflex reflectance properties are imparted to such relatively-smooth reflective surfaces without materially destroying the normal daytime appearance of the surface. Characteristically, on application by spraying, my composition becomes mobile but clings to its applied surface while shifting of the microspheres takes place. They move about in the applied layer; and the microspheres form themselves into a tightly compacted monolayer in tangential contact with the underlying surface. The varnish non-volatiles settle down about the microspheres and leave their outer hemispherical portion essentially free of a varnish coating. Such result contributes greatly to the elficiency of the microspheres as lens elements for the concentration and refraction of light Without interference from the binder. The varnish binder in general has a lower refractive index and is not essentially relied upon in my resulting structures for its light refractive properties.

The following example will serve to illustrate my invention, but is not to be construed as limitative thereof.

Parts by Weight Glass microspheres having a refractive index of about 1.9 and diameters between approximately A pol-yarnide modified alkyd resin, which is desirable because of its thixotropic properties, is available under the trademark Burnok 3712, and is believed to be disclosed in United States Patent 2,663,649. A suitable mineral spirits solvent commercially available is Shell solvent #140 which contains by weight about 68% of a mixture of paraffins, about 1% of a mixture of olefins, and about 31% of a mixture of naphthenes. This solvent boils in the range of about 364 F. to 407 F. (At about 368, of the mixture distills, and at 387, about 90% of its distills.) Metal naphthanate varnish driers are well known to the art, e.g., a mixture of cobalt, manganese and lead naphthanates. Anti-skinning agents are also well known in the varnish art (a suitable one being Exkin No. 1, containing the active ingredient butyraldoxime) and minimize the formation of a surface skin upon expo-sure to the atmosphere.

The composition is prepared by charging the alkyd resin gel to a mixing kettle and vigorously agitating. The naphtha and mineral spirits are slowly added with mixing and heating to 120 F. to obtain a smooth mixture. Then the metal naphthanate drier and anti-skinning agent are added and worked in. As the batch cools and becomes morc viscous, the glass microspheres are stirred 4- in and dispersed. Stirring tends to fluidize the composition, and termination of stirring allows the composition to slightly gel; the composition exhibits thixo-tropy.

The BVC of this composition is 69.6%. In other Words, the glass microspheres in this composition account for 69.6% of the total non-volatile or solids constituents (varnish solid-s plus glass microspheres) of the composition.

The composition has been sprayed upon a variety of underlying reflective surfaces. When sprayed, the composition becomes highly mobile; and of course, air is entrained with it. After application to a surface, it inherently forms, upon drying, a structure especially designed for maximum efficiency in terms of reflex reflection. Immediately after application to a surface, the glass microspheres flow out to form a closely nested layer essentially one bead in thickness (i.e., a monolayer). The microspheres cling in tangential contact to the applied surface. Thus the focal point of the beads is in proper position (i.e., directly in tangential contact with the reflective surface) for maximum cooperation with the underlying reflective surface to impart reflex reflection to the resulting structure. Varnish solids tend to roll off, or shrink away from the outer portion of the microspheres. As the varnish dries by solvent evaporation or by varnish polymerization or curing, the varnish solids simultaneously further migrate away from the upper or outer hemispherical surfaces of the microspheres exposing a 'lenticular surface to the atmosphere. At most, only an extremely thin skin of varnish solids remains on the outer hemispherical surface of the microspheres. Secure anchorage of the microspheres to the base surface is thus achieved and yet interference from the varnish solids is essentially obviated so that the microspheres can perform their light refracting and concentrating function With maximum efficiency.

My composition has been used to form, When sprayed and dried on an aluminized surface, durable reflex reflecting structures having a brightness as high as 550 times greater than that of white paint when tested under reflex-reflecting conditions. The total thickness of the coating of my preferred composition in such a structure has not exceeded about 2 mils.

It will be readily apparent that the small glass microspheres in my composition may be colored, Where it is desired to modify the color of a surface over which my composition is to be applied. For example, yellow glass microspheres 'may be utilized to impart a yellowish tint to an underlying surface, e.g., a metallic aluminum surface. Likewise, transparent colorants, e.g., phthalocyanine blue, may be added to the varnish vehicle. Small amounts of thixotropic agents such as, for example, alkyl ammonium montmorillcnite (Bentone 18C) may be mixed in my composition to improve its thixotropic properties; however, the amount of such thixotropic agents should not interfere with the essential transparent property of my composition and its ability to inherently form a brilliant reflex reflecting complex upon drying after application to a surface. Various varnish compositions satisfying the requirements hereof will be apparent to those skilled in the art after reading this disclosure. For example, cellulosicbase varnishes, alkyds, phenolics, etc., have all been found suitable, but usually need a small amount (e.g., up to about 4% by Weight of vehicle) of a thixotropic agent added thereto for properties as aforediscusscd.

That which is claimed is:

A fluidizable transparent varnish composition containing transparent glass microspheres and suitable for spray application upon a reflective base surface to provide upon drying a monolayer of transparent glass microspheres in intimate bonded tangential contact with said reflective surface and embedded in a transparent varnish film conforming to the microspheres to provide an exposed lenticular surface on the side of said monolayer facing outwardly of said reflecting surface, thereby to provide a composite structure exhibiting reflex reflection of incident light striking the same, said composition consisting essentially of a mixture of transparent thixotropic alkyd-baseresin-type varnish vehicle and small transparent glass microspheres having a diameter between approximately 15 and 60 microns and a refractive index of approximately 1.9, said transparent thixotropic varnish vehicle having a non-volatile solids content of between about 5 and 30% by weight and a corresponding volatile content of between about 95 and 70% by weight, said microspheres being present in an amount sufiicient to account for between 65 and 75% of the total volume of the non-volatile constituents of the composition, said composition further being transparent, mobile and exhibiting a viscosity on the order of rich cream upon agitation, with said microspheres being stably suspended and essentially uniformly distributed in said composition for usefully long periods without agitation.

References Cited in the file of this patent UNITED STATES PATENTS Heltzer Nov. 13, 1951 Nordlander et a1 June 9, 1953 Porth July 21, 1953 Schollick et a1 Oct. 21, 1958 Bolton et a1 Nov. 11, 1958 Hort May 19, 1959 Ialmquist et a1 Dec. 6, 1960 Searight Aug. 22, 1961 FOREIGN PATENTS Australia June 20, 1957 Great Britain Feb. 5, 1945 

1. FLUIDIZABLE TRANSPARENT VARNISH COMPOSITION CONTAINING TRANSPARENT GLASS MICROSPHERES AND SUITABLE FOR SPRAY APPLICATION UPON A REFLECTIVE BASE SURFACE TO PROVIDE UPON DRYING A MONOLAYER OF TRANSPARENT GLASS MICROSPHERES IN INTIMATE BONDED TANGENTIAL CONTACT WITH SAID RELECTIVE SURFACE AND EMBEDED IN A TRANSPARENT VARNISH FILM CONFORMING TO THE MICROSPHERED TO PROVIDE AN EXPOSED LENTICULAR SURFACE ON THE SIDE OF SAID MONOLAYER FACING OUTWARDLY OF SAID REFLECTING SURFACE, THEREBY TO PROVIDE A COMPOSITE STRUCTURE EXHIBITING REFLEX REFLECTION OF INCIDENT LIGHT STRIKING THE SAME, SAID COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF TRANSPARENT THIOXOTROPIC ALKYD-BASERESIN-TYPE VARNISH VEHICLE AND SMALL TRANSPARENT GLASS MICROSPHERES HAVING A DIAMETER BETWEEN APPROXIMATELY AND 60 MICRONS AND A REFRACTIVE INDEX OF APPROXIMATELY 1.9, SAID TRANSPARENT THIXOTROPIC VARNISH VEHICLE HAVING A NON-VOLATILE SOLIDS CONTENT OF BETWEEN ABOUT 5 AND 30% BY WEIGHT AND A CORRESPONDING VOLATILE CONTENT OF BETWEEN ABOUT 95 AND 70% BY WEIGHT, SAID MICROSPHERES BEING PRESENT IN AN AMOUNT SUFFICIENT TO ACCOUNT FOR BETWEEN 65 AND 755 OF THE TOTAL VOLUME OF THE NON-VOLATILE CONSTITUENTS OF THE COMPOSITION, SAID COMPOSITION FURTHER BEING TRANSPARENT, MOBILE AND EXHIBITING A VISCOSITY ON THE ORDER OF RICH CREAM UPON AGITATION, WITH SAID MICROSPHERES BEING STABLY SUSPENDED AND ESSENTIALLY UNIFORMLY DISTRIBUTED IN SAID COMPOSITION FOR USEFULLY LONG PERIODS WITHOU AGITATION. 